/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.tags;

import java.beans.PropertyEditor;
import java.io.IOException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;

import org.springframework.lang.Nullable;
import org.springframework.web.util.TagUtils;

/**
 * The {@code <transform>} tag provides transformation for reference data values
 * from controllers and other objects inside a {@code spring:bind} tag (or a
 * data-bound form element tag from Spring's form tag library).
 *
 * <p>The BindTag has a PropertyEditor that it uses to transform properties of
 * a bean to a String, usable in HTML forms. This tag uses that PropertyEditor
 * to transform objects passed into this tag.
 *
 * <table>
 * <caption>Attribute Summary</caption>
 * <thead>
 * <tr>
 * <th>Attribute</th>
 * <th>Required?</th>
 * <th>Runtime Expression?</th>
 * <th>Description</th>
 * </tr>
 * </thead>
 * <tbody>
 * <tr>
 * <td>htmlEscape</td>
 * <td>false</td>
 * <td>true</td>
 * <td>Set HTML escaping for this tag, as boolean value. Overrides the default HTML
 * escaping setting for the current page.</td>
 * </tr>
 * <tr>
 * <td>scope</td>
 * <td>false</td>
 * <td>true</td>
 * <td>The scope to use when exported the result to a variable. This attribute
 * is only used when var is also set. Possible values are page, request, session
 * and application.</td>
 * </tr>
 * <tr>
 * <td>value</td>
 * <td>true</td>
 * <td>true</td>
 * <td>The value to transform. This is the actual object you want to have
 * transformed (for instance a Date). Using the PropertyEditor that is currently
 * in use by the 'spring:bind' tag.</td>
 * </tr>
 * <tr>
 * <td>var</td>
 * <td>false</td>
 * <td>true</td>
 * <td>The string to use when binding the result to the page, request, session
 * or application scope. If not specified, the result gets outputted to the
 * writer (i.e. typically directly to the JSP).</td>
 * </tr>
 * </tbody>
 * </table>
 *
 * @author Alef Arendsen
 * @author Juergen Hoeller
 * @see BindTag
 * @since 20.09.2003
 */
@SuppressWarnings("serial")
public class TransformTag extends HtmlEscapingAwareTag {

    /**
     * the value to transform using the appropriate property editor.
     */
    @Nullable
    private Object value;

    /**
     * the variable to put the result in.
     */
    @Nullable
    private String var;

    /**
     * the scope of the variable the result will be put in.
     */
    private String scope = TagUtils.SCOPE_PAGE;


    /**
     * Set the value to transform, using the appropriate PropertyEditor
     * from the enclosing BindTag.
     * <p>The value can either be a plain value to transform (a hard-coded String
     * value in a JSP or a JSP expression), or a JSP EL expression to be evaluated
     * (transforming the result of the expression).
     */
    public void setValue(Object value) {
        this.value = value;
    }

    /**
     * Set PageContext attribute name under which to expose
     * a variable that contains the result of the transformation.
     *
     * @see #setScope
     * @see javax.servlet.jsp.PageContext#setAttribute
     */
    public void setVar(String var) {
        this.var = var;
    }

    /**
     * Set the scope to export the variable to.
     * Default is SCOPE_PAGE ("page").
     *
     * @see #setVar
     * @see org.springframework.web.util.TagUtils#SCOPE_PAGE
     * @see javax.servlet.jsp.PageContext#setAttribute
     */
    public void setScope(String scope) {
        this.scope = scope;
    }


    @Override
    protected final int doStartTagInternal() throws JspException {
        if (this.value != null) {
            // Find the containing EditorAwareTag (e.g. BindTag), if applicable.
            EditorAwareTag tag = (EditorAwareTag) TagSupport.findAncestorWithClass(this, EditorAwareTag.class);
            if (tag == null) {
                throw new JspException("TransformTag can only be used within EditorAwareTag (e.g. BindTag)");
            }

            // OK, let's obtain the editor...
            String result = null;
            PropertyEditor editor = tag.getEditor();
            if (editor != null) {
                // If an editor was found, edit the value.
                editor.setValue(this.value);
                result = editor.getAsText();
            } else {
                // Else, just do a toString.
                result = this.value.toString();
            }
            result = htmlEscape(result);
            if (this.var != null) {
                this.pageContext.setAttribute(this.var, result, TagUtils.getScope(this.scope));
            } else {
                try {
                    // Else, just print it out.
                    this.pageContext.getOut().print(result);
                } catch (IOException ex) {
                    throw new JspException(ex);
                }
            }
        }

        return SKIP_BODY;
    }

}
